The objectives are to: 1) Continue to maintain a registry established in 1972 to characterize and classify all spontaneous neoplasms from "veterinary-using" dogs and cats housed within a defined geographical area. Emphasis is placed on uniformity in case histories and a consistent histologic classification. 2) Continue to compare a "veterinary-using canine and feline population" from the same geographical area. For statistical interpretation the numerator will consist only of histologically diagnosed tumor. In the limits of the proposal this criterion can be met only when tissue is submitted to the Registry by a veterinarian. The appropriate denominator is the total "veterinary- using" dog and cat population of the area tabulated from hospital records. Consistency in histogenetic classification of tumors will be favored by restriction of tissue interpretation to three veterinary pathologists with interest in tumor histopathology, frequent consultation, and constant references to previous cases and the use of a cytologic criterionon tumor imprint and exfoliative cytologic specimens as well as conventional histologic sections. Variables such as age, sex status, breed, anatomic sites, biologic behavior of tumors, and geographic neighborhood can be included in distribution studies, as well as annual comparison of tumor distribution to detect trends. Hospital Registries of human tumors in this geographic area are available for limited comparison of data. Partial or complete data for adjunct studies requiring separate funding would be available. These include 1) Laboratory and investigative etiologic studies, 2) Human-animal associations particularly related to horizontal transmission of neoplasms involving dogs, cat and man. 3) Human-animal comparisons in which biologic behaviors of similar tumors in animals and man are studied.